Occurring both in plants and animals, sterols are a group of natural compounds, the most important of which are summarised in the following table:
Main phytosterols RΔ5-RΔ7-BrassicasterolΔ7- StigmasterolΔ7- CampesterolΔ7- Sitosterol Avenasterol

Nutritional studies confirmed that plant sterols decrease the cholesterol level of the blood serum and positively influence the ratio of the LDL and HDL cholesterol level (Westrate J A, Meijer G W. Plant sterol-enriched margarines and reduction of plasma total- and LDL-cholesterol concentrations in normocholesterolaemic and mildly hypercholesterolaemic subjects. European Journal of Clinical Nutrition 1998 52: 334-43; Miettinen T A, Puska P, Gylling H, et al. Reduction of serum cholesterol with sitostanol-ester margarine in a mildly hypercholesterolaemic population. New Engl. Journal of Medicine 1995;333:1308-1312). Plant sterols are applied predominantly in the food, pharmaceutical and cosmetic industry.
Tocopherols and tocotrienols (in general tocol compounds) possess vitamin E activity, the highest level is exhibited by α-tocopherol.
Tocopherols have important role in the human organism, due to their antioxidant properties they act as free radical scavengers and they also bind the molecular oxygen (A. Kamal-Eldin and L. A. Appleqvist: The Chemistry and Antioxidant properties of Tocopherols and Tocotrienols. Lipids 31. (1996) 671-701.).
The concentration of sterols and tocopherols in vegetable oils is too low to allow their industrial recovery in an economical way. At industrial scale natural sterols and tocopherols are obtained from the so-called deodorization distillate formed during refining of vegetable oils.
Vegetable oils are most widely refined by applying chemical or physical refining processes. In the last step of both processes, the oil is subjected to vacuum-steam distillation in order to remove the taste and odoriferous materials as well as the free fatty acids and also to improve the oxidative stability of the oil. Deodorization is generally performed at a temperature of 210-270° C., under reduced pressure (1-8 mbar), the deodorization distillate is obtained by condensation of the vapours formed during the operation. Besides the main components, according to their volatility various other substances appear in the deodorization distillate, the composition of which can be characterised as follows:
free fatty acids30-85% unsaponifiable materials7-35%tocopherols 1-8%free sterols2-15%sterol esters 0-5%glycerides5-30%others 0-5%* the % values relate to weight %
Numerous processes are described for recovery of sterols and tocopherols from deodorization distillates. In several patents distillation is preferably applied to remove fatty acids or fatty acid methyl esters (EP 0 333 472, U.S. Pat. Nos. 5,424,457, 5,627,289, 4,454,329). A saponification process is suggested for free fatty acid removal in the following patents: U.S. Pat. No. 3,335,154, 4,550,183 and WO 99/42471.
According to U.S. Pat. No. 5,512,691 prior to the fatty acid distillation, the free sterols are esterified with the fatty acids present in the deodorization distillate. The advantage of this step is that the boiling point range of the formed sterol esters is much higher than that of the unreacted tocopherols, which makes the separation of the two groups of compounds simple using short-path distillation.
According to U.S. Pat. No. 5,487,817 crystalline free sterols can be recovered from the sterol esters concentrated in the residue of the distillation.
Esterification of the free sterols with the free fatty acids present in the deodorization distillate requires relatively high temperature (150-250° C.), long reaction time (1-12 hours) and reduced pressure (lower than 50 mbar), in some cases application of acidic type catalyst is necessary. As a consequence of the unfavourable conditions (high temperature, long reaction time), unwanted side-reactions take place, such as degradation of tocopherols, transformation of sterols into hydrocarbons by losing the functional —OH group and a H atom as water, and increased formation of tar.